JPH07111940B2 - Method for joining semiconductor substrates - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for joining semiconductor substrates in which two semiconductor substrates are firmly joined and integrated.

[Prior art]

Accurate and reliable formation of portions having different impurity concentrations on a semiconductor substrate is an essential and most basic technique for manufacturing a semiconductor device. For that purpose, methods such as diffusion, ion implantation, and epitaxial growth have been conventionally used.

[Problems to be solved by the invention]

However, in such a conventional impurity introduction technique, in the case of forming a thick layer of, for example, several hundreds of μm, it is not possible with a normal ion implantation technique or a diffusion technique, and the epitaxial method requires an extremely long time. There was a problem that it was not economical.

Also, in the case of pressure sensors made of silicon,
Conventionally, for example, a method of using a low melting point glass has been used for bonding the diaphragm and the substrate, but since the bonding strength is weak and the coefficient of thermal expansion is greatly different between silicon and glass, it is difficult to heat There is a problem that the joint portion is easily broken by the stress.

In addition, a method of joining semiconductor substrates having different impurity concentrations using an ordinary polymer adhesive or the like is also conceivable, but in this method, ohmic joining cannot be performed and a large amount of foreign matter is mixed into the substrate. was there.

Further, as described in Japanese Patent Laid-Open Publication No. 51700 in 1985, there is also a method of bonding the two silicon crystal bodies to each other after mirror-polishing the bonding surface, hydrophilic treatment and drying, In the method, the two crystals are fixed immediately after they are joined together, so the position cannot be moved once they are joined together, making it difficult to align them. The joint surface is exposed and scratched. Easy,
In addition, it is difficult to keep the surface clean.If air remains on the joint surface, nitrogen molecules and oxygen molecules in the air do not easily diffuse even by a high temperature heating operation of about 1000 ° C. Therefore, there is a problem that it is necessary to work under vacuum.

The present invention is intended to solve the problems of the prior art as described above.

[Means for solving problems]

In order to achieve the above object, in the present invention, each bonding surface of the two semiconductor substrates is mirror-polished, and a solute-free liquid that contributes to the precipitation of a solid phase, that is, a solid precipitates when dried The two semiconductor substrates are bonded to each other by bringing them into intimate contact with each other through a thin film of a non-existing liquid and applying heat treatment. The above heat treatment is performed at a temperature considerably lower than the melting point of the semiconductor substrate.

With the above-mentioned configuration, in the present invention,
The two semiconductor substrates can be integrated at the bonding interface having a strength similar to that of the bulk, and at the same time, ohmic bonding can be performed.

Also, since they are bonded via a thin film of liquid, they can be easily moved to each other's position after they are aligned. Therefore, it is extremely easy to align the wafers without damaging the polished surfaces of both wafers. I can. Further, since the surface is covered with a thin film of liquid, it is easy to keep the surface clean, and it is not necessary to work under vacuum. In addition, since it is incompressible, it is easy to form a thin film with a uniform thickness between wafers, which is suitable for mass production. Further, the wafer bonding surface can be preliminarily treated as long as the bonding surface is mirror-polished, and it is extremely simple without any need to touch a commercially available wafer.

Example of Invention

 Hereinafter, the present invention will be described based on examples.

(A) First Example In this example, a single crystal semiconductor substrate (for example, single crystal Si
Substrate) Joins one another.

Commercially available semiconductor wafers used in the manufacture of conventional semiconductor devices have mirror-polished main surfaces on which elements are formed.

In this example, commercially available 3 inch and 2 inch silicon wafers that had been mirror-polished as described above were used. First, 0.3 μm particles were used to set a class 1000 (1000 particles / f).
In a clean room of t ³ ), methyl alcohol was dripped on the mirror surfaces of the two silicon wafers to wet the whole. By the way, even a water-repellent mirror surface that was not well wetted with water could be well wetted by using a solution containing alcohols mainly containing methanol, acetic acid, formic acid, and ammonia.

As the liquid used at this time, it is necessary to use a liquid that does not contain a solute that contributes to the precipitation of the solid phase, that is, a liquid that does not precipitate a solid when dried.

Next, the surfaces that were still wet with methanol, that is, the surfaces on which a thin film of methanol had been formed, were brought into close contact with each other without the inclusion of bubbles.

At the beginning, when both wafers are in close contact with each other, it is extremely easy to move them horizontally, but after sliding them several times, they can be left at a desired position for a certain period of time under a pressure of several 100 g / cm ³ or less. Both wafers are firmly integrated and cannot be easily peeled off. It should be noted that when the mutual slide is repeated, they are brought into close contact with each other without being left under pressure.

In addition, after uniformly wetting the polishing surface of one wafer with the liquid, align the polishing surface of the other wafer so that air bubbles do not enter, and leave it horizontally on a hot plate at around 50 ° C for several hours or longer. Then, the two wafers will come into close contact with each other while the orientation flats are naturally aligned.

The above-mentioned fixed state is quite strong, and even if the tip of the sharp stainless steel tweezers is twisted at the place where it seems to be the boundary surface of what is intimately adhered and integrated, it can not be easily peeled off, and it was successfully peeled off. However, the silicon substrate itself was often damaged by the tweezers.

In addition, on the mirror surface of the wafer peeled off as described above,
Interference fringes of methyl alcohol were observed.

Further, according to the weighing method, the thickness of the methanol thin film was several μm or less.

All the above operations were performed at room temperature.

Next, the two wafers that were adhered and integrated with each other through the methanol thin film were heat-treated at about 100 ° C. for about 30 minutes, and further heated at about 1000 ° C. for about 90 minutes using a heating furnace with N ₂ gas ventilation. .

The joint interface thus obtained was sufficiently strong, and a compression shear fracture test was performed on a piece cut into a square with a side of 2 mm by a dicing saw, and a fracture strength of 70 to 90 kg / cm ² was obtained. . When the broken pieces were observed, they were hardly separated from the bonded surface into two pieces, and many pieces were formed. From this, it can be seen that the two wafers are almost integrated.

Further, it also showed good ohmic characteristics electrically.

In addition, when the heating temperature was changed and tried, it was found that the bonding strength was approximately the same as that obtained at 1000 ° C. at about 500 ° C. or higher.

Next, the operation will be described.

Conventionally, it is often observed that the two surfaces come into close contact with each other when they are brought into contact with each other via a liquid thin film, and if the polishing state is good, it is also possible to have a considerable adhesiveness without a liquid film. It is being observed. In particular, it is often observed that the polishing surfaces of silicon wafers have a considerable adhesiveness. These have long been known as the mirror effect. It is said that the flatness of the polished surface of a commercially available silicon wafer is within several hundred liters.
It is believed that this has the effect of increasing this mirror effect.

However, it is unlikely that the two silicon wafers are in close contact with each other only due to the mirror effect due to the capillary phenomenon due to the negative pressure. That is, it is a common theory that the surface of silicon is covered with a natural oxide film in a natural environment. However, it is generally considered that the film thickness is an adsorption layer close to a monolayer film. The oxide film having a thickness of 20 Å or more was not formed even by the inventor's actual measurement. It is established that this oxide film has a silanol group in which a hydroxyl group is bonded to a dangling bond of silicon atoms on the surface.
It is also a dogma that the silanol group easily bonds with water in the air and forms a hydrogen bond. It is presumed that these liquids having an association property with hydrogen-bonded water are bonded by the action of 1.5-2.0 times the normal hydrogen-bonding energy between molecules and the intermolecular force. Moreover, when the associative liquid is in the form of a thin film between solids, the interaction with the solid interface is stronger than the interaction between liquid molecules due to the structure of the liquid bulk, and the information is easily received by the liquid thin film. Even when heated, the transformation from its structural properties does not go through the usual form of liquid-gasification expansion (in this form, two wafers are separated or destroyed), but as if by the interaction of the interfaces. It is presumed that the distinction between liquid and solid will disappear, and that the route will be to rapidly diffuse from the liquid into the solid. Therefore, negative pressure is generated and the interface is further densified.

It is said that water has the strongest structural property among associative liquids, but if water is used instead of methanol to bond silicon wafers, it may break if the contact wafer is heated to several 100 ° C. Occasionally it happened. This is because the structure of water is too strong, so that it does not become a sufficiently thin film at the time of adhesion, or because the water has changed and expanded according to the normal transformation, or because the structure is too strong, the change is concentrated at the critical point, It is considered that the so-called bumping phenomenon occurred. This is because the interaction between water molecules is stronger than the interaction between the silicon surface and water during heating, and the activated molecules in the bulk of the water film cut off the structural properties of the interface. It is presumed that it causes a rapid expansion in the weak water bulk. This is presumed from the fact that when acetic acid or ammonia water, which has a weaker structure than water, is used instead of methanol, two favorable silicon bonded bodies were obtained as in the case of methanol.

In addition, the state of the Si surface changes due to heating, violent silanol groups vibrate as is known on the silica surface,
Cause decomposition dehydration reaction of the alcohol from the two OH groups of one molecule of water to produce well-known MeOH + SiOH → Me-O- Si + H 2
An esterification reaction of O occurs, and each element decomposed further into monomolecules diffuses in the Si bulk, silicon on both surfaces of the wafer bonds with Si-O-Si, and finally with Si-Si. It is supposed to be combined. In addition, at this time, it is conceivable that the liquid film may serve to flatten the micro cavity structure at the interface.

Further, it is expected that the liquid film at a higher temperature is different from a normal liquid, and a mechanism in which Si atoms are dissolved and diffused therein can be imagined.

Even if the surface of the silicon semiconductor is water-repellent, it adheres by a negative pressure through the liquid, and if the adhesiveness is high to some extent, it is considered that the interaction with the structural liquid increases during the heating. It is speculated that the bodies become joined during heating. This is consistent with the fact that it has been confirmed that both water-repellent wafers treated with fluorine can be bonded by the above method. However,
In this case, the yield of success was not so good when the intervening liquid was water.

Silicon wafer bonding has an association property of acetic acid, formic acid, ethanol, ammonia water, water, etc. instead of methanol,
It was confirmed that this can also be performed when a liquid containing a liquid having a large structural property is used.

FIG. 1 shows a scanning electron micrograph of the bonded surface at a magnification of 10,000.

As described above, in the first embodiment, the polishing surfaces of the two semiconductor substrates are brought into close contact with each other through the thin film of the solute-free liquid that contributes to the precipitation of the solid phase, and the melting point of the solid allows a low temperature. Since the method of joining is performed by heating the two semiconductor substrates, the two semiconductor substrates can be integrated at the joining interface having the same strength as the bulk strength, and at the same time, ohmic joining can be performed.

Also, since they are bonded via a thin film of liquid, they can be easily moved to each other's position after they are aligned. Therefore, it is extremely easy to align the wafers without damaging the polished surfaces of both wafers. I can. Further, even if pre-treatment cleaning is performed before wafer bonding, it is likely to be contaminated with rubber or the like in the subsequent drying process. However, in the present invention, the drying process that is most likely to be contaminated is unnecessary, and therefore the surface can be easily kept clean. Further, it is not necessary to perform the contacting work under vacuum in order to prevent air or the like that does not easily diffuse even by the heat treatment from entering between the wafers when the wafers are contacted. Further, since the material used for adhesion is a liquid and is incompressible, it is easy to form a thin film with a uniform thickness between the wafers, which is suitable for mass production. In addition, it is sufficient that the bonded surface of the wafer is preliminarily treated as long as the bonded surface is mirror-polished, and it is extremely simple without requiring any modification of the commercially available wafer.

(B) Second Embodiment In this embodiment, at least one of the two semiconductor substrates is
The one having a polycrystalline semiconductor film on the surface on the joining side is joined, whereby a polycrystalline layer can be formed in a single crystal substrate.

In a conventional semiconductor process, a so-called sandwich structure of single crystal-polycrystal-single crystal in which a polycrystal is deposited on a single crystal substrate and a single crystal is further formed on it cannot be manufactured. However, for example, in the conductivity modulation MOSFET as shown in FIG. 2, if the above sandwich structure can be formed, the polysilicon recombination region 3 contains a large amount of carrier recombination centers, which is extremely effective in preventing latch-up. There is an effect. In addition, this interlayer polysilicon structure is
It also has a great effect on preventing latch-up of OS / IC. Therefore, it is extremely important to manufacture a single crystal-polycrystal-single crystal structure as a basis for manufacturing a highly reliable MOS IC device.

In this example, in order to realize a so-called sandwich structure of single crystal-polycrystal-single crystal as described above, a single crystal semiconductor substrate on which a polycrystalline thin film is deposited and a single crystal semiconductor substrate or a single crystal on which a polycrystalline thin film is deposited is formed. It is possible to manufacture a single crystal-polycrystal-single crystal structure by joining with a semiconductor substrate.

In this embodiment, first, the respective bonding surfaces of the two single crystal semiconductor substrates are mirror-polished, and then a polycrystalline film is formed on one or both of the two bonding surfaces, and the formed polycrystalline surfaces are formed. And a semiconductor mirror surface or a polycrystalline surface are welded together via a thin film of a solute-free liquid that contributes to the precipitation of a solid phase, and then heat treatment is applied to join the two substrates.

The details will be described below.

In this embodiment, a commercially available 3-inch silicon wafer whose surface is mirror-polished is used. First, a polysilicon film (polycrystalline silicon film) having a thickness of about 3000 Å is formed on one or both mirror surfaces of two silicon wafers. Was deposited. Deposition is LPCVD
According to, the deposition rate was about 100 Å / min with the mixed gas of SiH ₄ and He under the condition of 630 ° C. and 0.6 Torr.
Further, an annealing operation was performed using N ₂ gas at about 1000 ° C. for about 2 hours. Then, the surface roughness of this polysilicon film is set to 50
It was mirror-polished to 0 Å or less.

The thus-formed polysilicon film surface and the polished silicon surface (single crystal silicon) or the polysilicon film surfaces were brought into close contact with each other through a thin film of special grade methanol. The method was to wet the entire bonding surface of two wafers with methanol in a clean room of class 1000 setting with 0.3 μm particles. The polysilicon film surface or the silicon surface was easily wet by methanol. In this way, the surfaces of the wet surfaces were brought into close contact with each other while preventing the inclusion of bubbles. Immediately after they are brought into close contact with each other, both wafers are easy to move in the horizontal direction, but slide them horizontally while holding them down a few times, and then position the two wafers at the desired position under a pressure of several 100 g / cm ₃ or less. By allowing the wafers to stand still for a certain period of time or sliding them on each other more than once, both wafers were firmly integrated at a desired relative position and could not be easily peeled off.

In addition, after uniformly wetting the polishing surface of one wafer with the liquid, align the polishing surface of the other wafer so that air bubbles do not enter, and leave it horizontally on a hot plate at around 50 ° C for several hours or longer. Then, the two wafers will come into close contact with each other while the orientation flats are naturally aligned.

The above operations were all performed at room temperature.

Further, as the above liquid, instead of methanol, acetic acid, formic acid, ethanol, ammonia water, water, etc.,
It was confirmed that this can be performed even when a liquid containing a liquid having an association property and a large structural property is used. However, as the liquid used at this time, it is necessary to use a liquid that does not contain a solute that contributes to the precipitation of the solid phase, that is, a liquid that does not precipitate a solid when dried.

Next, the closely contacted and integrated wafer is heat-treated at about 100 ° C for 30 minutes, and further exposed to an N ₂ gas atmosphere at about 1000 ° C for about 12 minutes.
Heated for 0 minutes.

When the bonded body thus obtained is forcibly peeled off, in the case of bonding between the polysilicon surface and the silicon polishing surface, many parts of the polysilicon film are peeled off from the wafer surface which was originally formed and bonded. Adhered to the polished surface of the silicon.
Further, in the case of joining the polysilicon films, the polysilicon film was peeled off from the one wafer portion while being integrated, and adhered to the other wafer. From these facts, the strength of the deposited polysilicon film surface-silicon surface interface and the strength of the bonded polysilicon film surface-silicon surface interface are almost the same, and the polysilicon film surface-polysilicon film surface by bonding is almost the same. It was confirmed that the strength of the interface was almost the same as the strength of the polysilicon film itself. A bonded wafer was cut into a square of 5 mm on each side by a dicing saw, and a compression shear fracture test was carried out. As a result, a fracture strength of 20 to 40 kg / cm ² was obtained.

An n-type polysilicon layer was sandwiched between the p-type and n-type single crystal cut plates by this method, and its electrical characteristics were measured. As a result, the rectifying property was good, the breakdown voltage was sufficiently high, and the leakage current was sufficiently high. It was confirmed to be low.

As described above, according to this embodiment, the semiconductor substrate formed with the polycrystalline film or the substrate formed with the polycrystalline film and the single crystal substrate are provided with a solute-free liquid thin film that contributes to the deposition of the solid phase. By bringing them into close contact with each other and heating at a temperature much lower than the melting point of the solid, it is possible to obtain the effect that a substrate having a structure in which a polycrystalline layer is embedded in a semiconductor single crystal substrate can be mass-produced at low cost with good controllability.

Other effects are similar to those of the first embodiment.

(C) Third Embodiment In this embodiment, at least one of the two semiconductor substrates is
This is a method of joining those having a dielectric film on the surface on the joining side, whereby a semiconductor substrate having a dielectric burying layer formed therein can be manufactured.

As the element isolation method in the conventional semiconductor integrated circuit,
Although a method using a pn junction has been used for a long time, it is not possible to cope with the increase in isolation capacity and the reduction in device size as the degree of integration increases.

A dielectric isolation method is desirable as an element isolation method that replaces the above method. This is especially true when a high breakdown voltage element is included. For example, in a power IC that integrates an output stage power transistor and an IC that drives or controls it, it is necessary to electrically and reliably separate the power transistor and the drive or control IC part, but pn junction separation is sufficient. Often not.

However, when the conventional dielectric isolation method is used, it is not easy to wrap a part of the element with the dielectric. In particular, in order to electrically separate the element region from the substrate region, it is necessary to embed a dielectric layer in the substrate, but the conventional dielectric embedding method has many problems.

For example, a method known as a polycrystalline support structure dielectric isolation method is to form an element on a semiconductor substrate surface, perform lateral element isolation, and then lap the semiconductor substrate from the back surface to expose the lower portion of the element region. , A dielectric film such as an oxide film is formed here, and a polycrystalline silicon layer or the like to be a support is formed again. However, this method has many process restrictions, and polycrystalline silicon and single crystal are used. There is a problem that the substrate tends to warp due to the difference in thermal expansion of silicon.

Further, as another example, a polycrystalline or amorphous silicon film is formed on a dielectric layer formed on a single crystal substrate,
There is an SOI method in which the film is monocrystallized by heat treatment, laser light, electron beam, etc., but this method requires expensive equipment such as laser, electron beam, and the size of the single crystal to be formed. There are restrictions on pod quality and shape.

In this embodiment, at least one of the two semiconductor substrates has a dielectric film on the surface on the bonding side, so that the dielectric layer can be embedded inside the substrate inexpensively and reliably. Is possible.

In this embodiment, first, each of the bonding surfaces of the two semiconductor substrates is mirror-polished, and an oxide film (dielectric film) thicker than a natural oxide film is formed on one or both polished surfaces. By sticking the polished surface of the semiconductor substrate or the oxide film to each other through a thin film of a liquid that does not contain solute that contributes to the precipitation of the solid phase, and heating them in an oxidizing gas atmosphere, the two semiconductor substrates are mutually bonded. It is to join.

The details will be described below.

In this embodiment, a commercially available silicon semiconductor substrate is used,
First, about 10 mirror surfaces of one or both of two silicon wafers
An oxide film of 00Å was formed. The oxide film was formed by heating at about 1000 ° C. in an oxygen gas atmosphere.

The oxide film surface thus prepared and the polished silicon wafer surface or the oxide film surface were adhered to each other via a thin film of methanol. In this method, the entire bonding surface of two wafers was wetted with methanol in a clean room of class 1000 setting with 0.3 μm particles. The oxide film surface and the mirror-polished surface were easily wet with methanol.

Further, as the above liquid, instead of methanol, acetic acid, formic acid, ethanol, ammonia water, water, etc.,
It was confirmed that this can be performed even when a liquid containing a liquid having an association property and a large structure is used. However, as the liquid used at this time, it is necessary to use a liquid that does not contain a solute that contributes to the precipitation of the solid phase, that is, a liquid that does not precipitate a solid when dried.

Next, the surfaces wet with methanol were brought into close contact with each other so that bubbles were not mixed. Both wafers were easy to move horizontally immediately after they were put together, but they were firmly integrated at a desired relative position by sliding them a few times while holding them down a little, so that they could not be easily peeled off.

In addition, after uniformly wetting the polishing surface of one wafer with the liquid, align the polishing surface of the other wafer so that air bubbles do not enter, and leave it horizontally on a hot plate at around 50 ° C for several hours or longer. Then, the two wafers will come into close contact with each other while the orientation flats are naturally aligned.

According to the weighing method, the methanol thin film had a thickness of several μm or less.

All the above operations were performed at room temperature.

Next, the two closely adhered and integrated wafers were heat-treated at about 100 ° C. for 30 minutes, and further exposed to O ₂ gas or steam atmosphere for 120 minutes at 1000 ° C.

Forcibly peeling off the bonded body thus obtained, in the case of bonding the oxide film surface and the silicon polishing surface, many parts of the oxide film were peeled off from the wafer originally formed and bonded to the silicon polishing surface. It adhered. Further, in the case of bonding oxide films to each other, the oxide film was integrally peeled off from one wafer portion and adhered to the other wafer. From these, the strength of the interface between the deposited oxide film surface and the silicon surface and the strength of the interface between the oxide film surface and the silicon surface due to the bonding are almost the same, and the strength of the interface between the oxide film surface and the oxide film due to the bonding is oxidized. It was confirmed that the strength was almost the same as the strength of the film itself. For example, a wafer bonded with a dicing saw was cut into a square having a side of 5 mm and subjected to a compression shear fracture test. As a result, a fracture strength of about 25 to 40 kg / cm ² was obtained.

When the heating temperature was changed and tried, it became clear that the bonding strength was sufficient at about 700 ° C or higher.

As described above, in this embodiment, a thin film of a solute-free liquid that contributes to solid phase deposition is used for a semiconductor substrate formed with an oxide film to be a dielectric withstanding film or a substrate formed with an oxide film and a normal substrate. Since the two substrates can be tightly bonded together by heating them in an oxidizing gas atmosphere at a temperature much lower than the melting point of the solid,
An effect is obtained that a substrate having a structure in which a dielectric film (oxide film) is embedded in a semiconductor single crystal substrate can be manufactured inexpensively, easily, and with good controllability in large quantities. In addition, the pre-treatment of the bonding surface of the wafer before bonding is only the formation of an oxide film,
It is advantageous for mass production without having to modify the commercially available wafer.

The other effects are similar to those of the first embodiment.

(D) Fourth Embodiment In this embodiment, a groove is provided on the surface of at least one of the two semiconductor substrates on the junction side, and a dielectric substance is provided on the surface of the groove. This makes it possible to manufacture a semiconductor substrate in which a dielectric burying layer is formed, as in the third embodiment.

In this embodiment, first, a groove that opens at the end of the substrate is formed on the surface of the first semiconductor substrate that has been mirror-polished, and then the second semiconductor substrate that has been mirror-polished and the first semiconductor substrate described above. The polishing surfaces are adhered to each other via a thin film of a liquid that does not contain solute that contributes to the precipitation of the solid phase, and heat treatment is applied to bond them together.
A method for forming a dielectric film on the surface of the groove by injecting an organic polymer resin solution into the groove formed at the end of the substrate formed between the bonded substrates and then heating the bonded substrate Is.

The details will be described below.

FIG. 3 is a cross-sectional view showing the manufacturing process of this embodiment.

In this example, the commercially available one side was mirror-polished 2
Sheets of silicon wafers 21 and 30 were used.

First, as shown in (a), at least one of the grooves 22, 23, and 24 opened at the wafer end was formed on the polished surface of the silicon wafer 21. The method of forming these grooves was performed by wet or dry etching using photo-resist as a mask by photo-patterning. However,
In order to form a shape such as the groove 24, it is necessary to devise such that only the deep portion is first formed by the long etching and the remaining shallow portion is formed by the short etching.

Next, the entire mirror surface of these substrates was wetted with methanol in a clean room of class 1000 setting with 0.3 μm particles. After that, the surfaces, which are still wet with methanol, are brought into close contact with each other without inclusion of bubbles. Align both wafers by sliding them horizontally several times,
Both wafers are firmly integrated by leaving them under a pressure of several 100 g / cm ³ or less for several hours.

In addition, after uniformly wetting the polishing surface of one wafer with the liquid, align the polishing surface of the other wafer so that air bubbles do not enter, and leave it horizontally on a hot plate at around 50 ° C for several hours or longer. Then, the two wafers will come into close contact with each other while the orientation flats are naturally aligned.

All the above operations are performed at room temperature.

It was confirmed that, as the above liquid, a liquid having an associative property such as acetic acid, formic acid, ethanol, ammonia water, and water was used instead of methanol. However, as the liquid used at this time, it is necessary to use a liquid that does not contain a solute that contributes to the precipitation of the solid phase, that is, a liquid that does not precipitate a solid when dried.

Next, the two wafers 21 and 30 that have been brought into close contact with each other and integrated together are heated to about 100 ° C.
Heat for 30 minutes at about 1000 in a heating furnace with N ₂ gas flow.
Heated at ℃ for about 90 minutes.

The interface of the bonded body thus obtained was sufficiently strong and almost matched the strength of the silicon bulk. In addition, it showed good electrical ohmic characteristics.

It has been confirmed that when the heat treatment temperature is about 500 ° C. or higher, the bonding strength almost matches the strength of the silicon bulk.

Next, as shown in (b), the wafer bonded body formed as described above was cut by polishing or the like to the position of the alternate long and short dash line to obtain a substrate 31 as shown in (c).

A desired element is formed on the substrate 31 manufactured in this manner. An integrated circuit can be obtained by performing a desired lateral element isolation by a usual semiconductor process technique.

Next, as shown in (d), the dielectric film 25 is formed. The order of this process differs depending on the heat resistance performance of the dielectric film forming molten resin used, but usually the element formation including the high temperature heat treatment process and the wiring formation process between them are over, PSG for them, nitride film etc. After formation of the protective film, the organic polymer resin is used.

In this example, "PIQ" (trade name, manufactured by Hitachi Chemical Co., Ltd.) as a polyimide-based resin and "imide-6001" (trade name, manufactured by Kanebo Co., Ltd., NNC) as a polyimide resin, "Fluorocoat" as a fluorine-based resin (Trade name, manufactured by Asahi Glass Co., Ltd.), fluorinated type THERMID resin "FA-7001" (manufactured by Kanebo Co., Ltd., NC)
However, the organic polymer resin solution for forming a dielectric is not limited to these.

In any of the above resin solutions used as the dielectric film forming method, first, a desired resin solution is injected into each groove, and the surface of each groove is covered as uniformly as possible.

There are various injection methods, but when a circular silicon wafer is used as an example, the other opening of the groove that opens at the wafer edge is provided in the center of the wafer, and the resin solution is injected there There is a method in which spin is added in saturated steam to spread the groove to the end. However, in the case of the shape such as the groove 23, uniform injection from the surface, that is, a so-called spin coating method is sufficient. The rotation speed was set to 6000 rpm in consideration of safety when using a 3-inch wafer.

The viscosities of the above resin solution products are as follows when expressed as CP as a standard at room temperature.

PIQ… 11 (14.5%) Solvent NMP / DMAc IP−6001… 28 (30%) 〃NMP / xylene Fluorocoat “EC-104”… 1.1 〃 CFC R-113 FA-7001… 50 (30%) 〃NMP / Xylene Therefore, depending on the shape and size of the groove, it may be necessary to add a solvent to reduce the viscosity. Further, the fluoro coat can be injected and attached in the form of an aerosol.

The heat treatment after the injection is carried out under the following conditions with nitrogen aeration.

PIQ …… 60 minutes at 200 ℃, then 30 minutes at 350 ℃ IP-6001… 60 minutes at 300 ℃, then 15 minutes at 400 ℃ Fluorocoat “EC-104” …… 3 hours at 60 ℃, then room temperature dry FA -7001 ... 60 minutes at 300 ° C., then 15 minutes at 400 ° C. The above treatments form the dielectric layers having the following desired performances.

PIQ relative permittivity (1kHz) 3.4 IP-6001 〃 〃 3.6 Fluorocoat “EC-104” 〃 〃 3.7 FA-7001 〃 〃 3.0 The shape and size of the groove may be variously formed according to the purpose. It does not matter how these are formed on any semiconductor substrate. In addition, the material for forming the dielectric is mixed or selected according to the shape and size of the groove.

Further, a portion where the organic film is not desired to be formed is removed by O ₂ plasma etching or the like after the formation.

Further, the film formed here can sufficiently withstand the temperature of about 200 to 350 ° C. in the wire bonding treatment of the post treatment.

Further, if formation of elements, pipes and the like is possible at a temperature within the heat resistant range of the resin, the elements and wirings may be formed after the formation of the dielectric by the resin.

As described above, in this embodiment, it is possible to obtain the effect that a large amount of the dielectric burying layer can be manufactured inside the semiconductor substrate easily, inexpensively and reliably.

In addition, depending on the shape of the groove to be formed, an organic film is naturally formed on the part other than the groove, for example, on the element, but this is effective as a passivation film, and at the same time as the element isolation film is formed, corrosion protection and mechanical stress are applied. There is an advantage that a protective film can be formed.

Other effects are similar to those of the first embodiment.

(E) Fifth Embodiment In this embodiment, an oxide film serving as a dielectric is formed on the surface of the groove instead of the dielectric made of the organic polymer resin in the fourth embodiment.

FIG. 4 is a cross-sectional view showing the manufacturing process of this embodiment, and the same reference numerals as those in FIG. 3 indicate the same parts.

In FIG. 4, first, as in the case of FIG. 3, a bonded body of the substrates 21 and 30 having grooves is formed. Next, (b)
An oxide film is formed on the surfaces of the grooves 22, 23 and 24 of the joined body of the substrates 21 and 30 as shown in FIG. This forming method includes, for example, a coating liquid for forming a SiO ₂ film known as spin-on-glass.
OCD (trade name Tokyo Ohka Kogyo Co., Ltd.) and Si (OR) ₄
The alkoxide of Si represented by the above is dissolved in an organic solvent such as ethanol, and water for hydrolysis and an acid or a base are added, if necessary, to prepare the solution.

The former uses, for example, Si having a wt% of 5.9, and the latter uses, for example, the following solution distribution.

Ethyl silicate _{Si (OC 2 H 5) 4} 1mol water (H ₂ O) 500cm ³ hydrochloric acid (HCl) 0.02 mol of ethanol 300 cm ³ Note that the mixed solution was made uniform at reflux for example 2 hours at 90 ° C. Will use later.

In the method of forming an oxide film to be a dielectric, first, a coating solution for forming a SiO ₂ film was injected into the groove portion, and the surface of each groove was covered as uniformly as possible. There are various injection methods, but when using a circular silicon wafer as an example, the other opening that communicates with the groove that opens to the edge of the wafer is provided in the center of the wafer, and the coating solution is injected from there. The spin was added in a saturated vapor of solvent to reach the end of the groove. The number of rotations of the spin is, for example, 5000 to 6000 rpm in consideration of safety.

An oxide film (SiO ₂ film) 26 is formed on the surface of the groove by performing a heat treatment after the implantation, and the conditions are as follows, for example.

OCD: 30 minutes at 150 ° C, then 900 ° C for 30 minutes in a nitrogen atmosphere Si alkoxide solution: 120 minutes at 120 ° C in a nitrogen atmosphere, then 60 minutes at 600 ° C The latter is Si (OC ₂ H ₅ ) ₄ + 4H ₂ O → Si (OH) ₄ + 4C ₂ H ₅ OH Si (OH) ₄ → SiO ₂ + 2H ₂ O ↑ SiO ₂ is formed by the reaction.

Next, the substrate 31 as shown in (c) is obtained by cutting to the position indicated by the alternate long and short dash line in (b) by means such as polishing.

Furthermore, an integrated circuit can be obtained by performing desired lateral element isolation and element formation by ordinary semiconductor process technology.

Note that the oxide film forming liquid is not limited to those listed here.

The shape and size of the groove may be variously formed according to the purpose, and these may be formed on any semiconductor substrate in any way. In addition, the material for forming the dielectric is mixed or selected according to the shape and size of the groove.

As described above, in this embodiment, the effect that the oxide film (dielectric-embedded layer) can be easily and inexpensively manufactured inside the semiconductor substrate with high reliability can be obtained.

Other effects are similar to those of the first embodiment.

In addition, in the fourth and fifth embodiments, when forming the dielectric burying layer, a substance that is liquid at room temperature is used. This means that when a gas is used as the material, a dielectric such as an oxide film is likely to be selectively formed at the gas inlet, and the opening is blocked before the inner groove surface is sufficiently oxidized. The effect is that it does not occur.

〔The invention's effect〕

As described above, in the present invention, two semiconductor substrates can be integrated at the bonding interface having the same strength as the bulk strength and can be simultaneously ohmic bonded. Also, since they are bonded via a thin film of liquid, the positions of them can be easily moved after they are aligned, so that the alignment of the wafers can be performed extremely easily without damaging the polished surfaces of both wafers. I can. Further, even if pre-treatment cleaning is performed before wafer bonding, it is easily contaminated with dust or the like in the subsequent drying process, but the present invention does not require the drying process that is most likely to be contaminated, and thus the surface can be easily kept clean. Further, it is not necessary to perform the contacting work under vacuum in order to prevent air or the like, which is not easily diffused even by the heat treatment, from entering between the wafers during the contacting of the wafers. Further, since the material used for adhesion is a liquid and is incompressible, it is easy to form a thin film with a uniform thickness between the wafers, which is suitable for mass production. In addition, the wafer bonding surface can be preliminarily treated as long as the bonding surface is mirror-polished, and there are many excellent effects such as the fact that it is extremely simple without the need to touch a commercially available wafer.

In addition, in the second embodiment, in addition to the above effects,
An effect is obtained that a substrate having a structure in which a polycrystalline layer is embedded in a semiconductor single crystal substrate can be mass-produced inexpensively with good controllability.

Further, in addition to the above effects, the third to fifth embodiments have the effect that a substrate in which a dielectric burying layer is formed in a semiconductor single crystal substrate can be manufactured inexpensively, easily, and in large quantity with good controllability. can get.

[Brief description of drawings]

FIG. 1 is an electron micrograph of a bonding surface of a semiconductor substrate bonded by the method of the present invention, FIG. 2 is a sectional view of an example of a MOSFET suitable for applying the present invention, and FIGS. 3 and 4 are respectively. It is an example of a manufacturing process of the present invention. <Explanation of symbols> 21 ... First silicon substrate 22, 23, 24 ... Groove 25 ... Dielectric film 26 ... Oxide film (dielectric film) 30 ... Second silicon substrate 31 ... Bonded Board

Claims (5)

[Claims] 1. The above-mentioned two semiconductor substrates are obtained by mirror-polishing respective bonding surfaces of the two semiconductor substrates, bringing them into close contact with each other through a thin film of a liquid containing no solute that contributes to precipitation of a solid phase, and applying heat treatment. A method of joining semiconductor substrates, the method including joining the substrates to each other. 2. The method for joining semiconductor substrates according to claim 1, wherein both of the two semiconductor substrates are single crystal substrates. 3. The method for bonding semiconductor substrates according to claim 1, wherein at least one of the two semiconductor substrates has a polycrystalline semiconductor film on the surface on the bonding side. 4. The method for joining semiconductor substrates according to claim 1, wherein at least one of the two semiconductor substrates has a dielectric film on the surface on the joining side. 5. A groove is provided on the surface of at least one of the two semiconductor substrates on the bonding side, and a dielectric substance is provided on the surface of the groove. The method for joining semiconductor substrates according to item 1.